This invention relates to novel flame retardants and more particularly it relates to flame retardants comprising alkali metal salts or (and) alkaline earth metal salts of specified phosphorus compounds.
Organic high molecular weight materials are usually easily combustible and it has recently been socially required to make these materials flame retardant. Thus, many flame retardants or flame retardant techniques have already been proposed or practically employed. However, when organic high molecular weight materials are made flame retardant by the use of flame retardants, it is usually necessary to add them in an amount of several % to ten and several %, hence there has been a draw back that physical or chemical characteristic properties intrinsic of organic high molecular weight materials as substrate are more or less harmed. On the other hand, among elements constituting flame retardants, halogens, phosphorus, antimony, nitrogen, etc. have heretofore been regarded as useful, but according to a series of recent patents, it has been found that an extremely small amount of alkali metal or alkaline earth metal compounds added to aromatic polycarbonate resins imparts a satisfactory, specific flame retardancy (see U.S. Pat. Nos. 3,775,367; 3,909,490; 3,917,559; 3,919,167; 3,926,908; 3,931,100; 3,933,734; 3,940,366; 3,948,851; 3,951,910; 3,953,396; 3,953,399; 3,978,024; 4,001,175; 4,007,155; 4,028,297; 4,032,506; 4,033,930; 4,039,509; and 4,064,101). However, the flame retardants disclosed in these patents also have two serious drawbacks. The first drawback is that since the compatibility of the flame retardants with substrates is inferior, the resulting resin compositions rendered flame retardant are generally opaque. In order to overcome such a drawback, there has been made an attempt to have the resulting compositions retain transparency although they are heterogeneous, by selecting flame retardants exhibiting the same refractive index as those of substrates (see U.S. Pat. Nos. 4,001,175; 4,007,155; and 4,039,509). Another drawback is that flame retardants are thermally unstable and have a tendency to be decomposed at high processing temperatures of the resulting resin compositions, and as a result, the molecular weights of substrates are reduced by the resulting decomposition products, resulting in a tendency to degrade characteristic properties such as impact-resistance.